By Keely Sudhoff, PhD

Sweet, salty, bitter, sour, and umami: these are the five
basic tastes our visitors learn about as part of the museum's
Genetics of Taste research project. It is the finely tuned
array of these taste qualities which allows us to savor tasty meals
or to take a sip of spoiled milk and toss it quickly down the
drain. We do not think about our actions; they are innate and
we are primed to know the difference. We taste for survival -
bitter can alert us to poisons; sweet signals a large intake of
energy (mmm, chocolate cake); umami informs us of savory proteins;
salty helps us maintain cellular balance.

Scientists know we taste for survival but have wondered how
taste messages are sent from the tongue to the brain. Charles
Zuker, a neuroscientist at Columbia University, is making
breakthroughs in understanding this pathway. He was
responsible for discovering the "one taste, one cell" system in
mammals (Chandrashekar et al. Nature 444, 288 (2006),
Yamolinsky et al. Cell 139, 234 (2009)). In
short, he concluded that the taste cells in our tongue are highly
specific, each cell expresses receptors that can only bind one
basic taste. After the target taste molecule binds it's
receptor in the taste cell, a neural pathway then sends the signal
to the brain. But where in the brain?

Previous brain models for taste identification suggested a broad
pattern of neural recognition across taste qualities, but Zuker's
most recent publication in Science this month (p. 1262)
has shaken up the field of gustatory science. When artificial
saliva containing different compounds was applied onto the tongues
of anesthetized mice, Zuker's team was able to see discrete
clusters of nerve cells fluoresce based on the selective response
to the individual basic tastes of bitter, salt, sugar and umami.
Moreover, these clusters of taste-specific neurons were located in
precise and spatially segregated areas of the cortex (Figure
1). Interestingly, the researchers did not find
sour-selective neurons. Zuker reasoned that this may be
because those neurons exist outside the region of the cortex they
surveyed.

So while we know for sure there is no taste map on the tongue,
evidence suggests that there may be one in the brain.